Human Parasites, From the Ones in Your Bed to the Ones You Get by Prescription

10,773 Number of protein-coding genes possessed by Pediculus humanus humanus (L.), the human body louse, according to a new study. Ten of those genes code for odor receptors, which researchers anticipate could become targets for future louse repellents. With 108 million DNA base pairs, the louse has the smallest known insect genome.

98 Percentage of people worldwide who host Demodex folliculorum or Demodex brevis, the only two arthropod species that permanently colonize the human body. These microscopic, eight-legged mites live in the follicles of our eyelashes, eyebrows, and nose hairs, where they feed on dead skin cells and oil.

81 Percent increase in bedbug calls to pest-control companies in the United States between 2000 and 2010, according to the National Pest Management Association and the University of Kentucky. The banned insecticide DDT nearly drove these nocturnal, crevice-dwelling, biting insects to extinction nationwide during the mid-20th century, but they have recently staged a fierce comeback. New York City alone saw 10,985 bedbug complaints in 2009, up from 537 in 2004.

3 million Number of medicinal leeches produced each year at the International Medical Leech Centre in Russia. Hospitals around the world use the bloodsucking annelids—which have three jaws, each bearing 100 tiny teeth—for tasks such as stimulating circulation after the surgical re­attachment of a severed finger or ear. Leeches received FDA approval as a medical device in 2004.

250,000,000 Estimated number of malaria cases each year, according to the World Health Organization, resulting in nearly a million deaths, mostly of children under age 5. Other parasitic diseases with a huge public health impact include amoebiasis (which kills 100,000 per year), leishmaniasis (60,000), and schistosomiasis (20,000). Globally, about one in every four people hosts parasitic worms.